Patent Literature 1: JP 2011-030151 A (US 2011/0029704 A1)
For the travel control of a vehicle, a plurality of first electronic control units need to share various synchronous data acquired at substantially the same time. A known method in Patent Literature 1 permits a first electronic control unit to act as a master node and periodically transmit a reference message to a communication line, and allows a first electronic control unit to receive the reference message and transmit synchronous data in response to the received reference message.
Additionally TTCAN (ISO 11898-4) and FlexRay (registered trademark) are also known as a time trigger method in which a master node transmits periodically a period start signal so that synchronous data is transmitted at a predetermined time based on the period start signal.
If a transmission line (hereinafter referred to as the first communication line) for transmitting synchronous data is broken or a communication transceiver is faulty during the use of the above conventional methods, the synchronous data cannot be communicated through the first communication line. This signifies that the synchronous data cannot be shared between the first electronic control units, adversely affecting the travel control.
If an employed communication system includes a second communication line in addition to the first communication line, the synchronous data may be shared through the second communication line. However, the second communication line is connected not only to the first electronic control unit but also to a second electronic control unit. For example, CAN (Controller Area Network), which is standardized by ISO 11898-1, is commonly known as a communication method using the second communication line. The communication method using the second communication line assigns priorities to data to be transmitted from individual electronic control units, and performs arbitration based on the assigned priorities to establish communication between preselected electronic control units. However, the communication method using the second communication line is of an event-driven type that does not achieve synchronization between various data.
When the communication through the first communication line is abnormal, the master node may periodically transmit a high-priority reference message through the second communication line and permit the first electronic control unit to receive the reference message and successively transmit synchronous data at a predetermined time based on the reception of the reference message. This provides synchronous communication; however, asynchronous data is lost in arbitration to unduly delay its transmission.